*CLYNN@G.BBN.COM*

*5 Oct 1987 16:28-EDT*

**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Next message:**Tim K telnet use: "NCSA Telnet version 2.0 available"**Previous message:**Gregory Lauer: "Re: TCP and Loss (inherently lossy nets)"

Mark,

One could, given suitable hardware, etc. compute the checksum more

than 16 bits at at time - e.g., use 32-bit arithmetic (or some other higher

number). There are at least two ways - adding 16 bits into a wider accumulator

which reduces/eliminates checking for carry/overflow, or adding 32 bits at a

time into the accumulator, reducing the number of memory fetches/adds/carry

checks by a factor of 2 (more if you have 64 bit arithmetic, etc.).

One can also compute the checksum as the data is being placed

into the packet, instead of computing it after the packet has been "built".

On retransmissions/repacketizations, one can "update" the checksum

(subtract out the old (header) values and add in the new) instead of

recomputing the sum of the data each time (the checksum is weak enough that

byte-pair position, order of summation, etc. doesn't matter).

**Next message:**Tim K telnet use: "NCSA Telnet version 2.0 available"**Previous message:**Gregory Lauer: "Re: TCP and Loss (inherently lossy nets)"

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